Method for manufacturing a lithium ion secondary battery and lithium ion secondary battery

Abstract

To provide a manufacturing method of a lithium ion secondary battery, enabling suppression of formation of a NaBOB coated film, and to provide the lithium ion secondary battery.SOLUTION: A manufacturing method of a lithium ion secondary battery includes: a positive electrode plate manufacturing step of manufacturing a positive electrode plate having a positive electrode mixture layer 23 which includes a positive electrode active material 31, a lithium hydroxide 32, and a lithium acetate 34; a negative electrode plate manufacturing step of manufacturing a negative electrode plate having a negative electrode mixture layer 26 which includes a negative electrode active material 41 and a sodium salt 42; and a step of injecting a non-aqueous electrolyte EL including LiBOB into a case in which the positive electrode plate and the negative electrode plate are housed. When the mol number of the lithium hydroxide 32 added in the positive electrode plate manufacturing step is A, the mol number of the lithium acetate 34 formed in the positive electrode plate manufacturing step is B, and the mol number of the sodium salt 42 added in the negative electrode plate manufacturing step is C, each value of A, B, and C satisfies 0.04≤B / A≤0.06 and 1.9≤B / C, and the lithium acetate 34 has a high solubility with respect to the non-aqueous electrolyte EL than that of a sodium acetate 50.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a lithium - ion secondary battery using a non - aqueous electrolyte containing LiBOB and a lithium - ion secondary battery.

Background Art

[0002] In a lithium - ion secondary battery, a SEI film (Solid Electrolyte Interface) is formed on the surface of the negative electrode mixture layer. The SEI film incorporates lithium ions during its formation process. Therefore, when the SEI film thickens due to repeated charge and discharge or long - term storage of the battery, the lithium ions contributing to charge and discharge decrease, resulting in a reduction in battery capacity.

[0003] To address this problem, a technique of adding lithium bis(oxalato)borate (LiBOB, LiB(C 2 O 4 ) 2 ) to the non - aqueous electrolyte is known. By adding LiBOB to the non - aqueous electrolyte, a stable film derived from bis(oxalato)borate ions (BOB ions, B(C 2 O 4 )2 - ) ionized from LiBOB can be formed on the particle surface of the negative electrode active material particles. Thereby, the growth of the SEI film can be suppressed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On one hand, the BOB ions ionized from LiBOB react with the sodium ions contained in the negative electrode binder layer to form a NaBOB film on the surface of the negative electrode binder layer. The sodium ions are derived from, for example, carboxymethyl cellulose (CMC) used as a dispersant and thickener in the negative electrode binder layer. Since the NaBOB film is one of the factors increasing the resistance of the negative electrode binder layer, it is desirable to suppress its formation.

Means for Solving the Problem

[0006] A method for manufacturing a lithium-ion secondary battery for solving the above problems includes a positive electrode plate manufacturing step of manufacturing a positive electrode plate by forming a positive electrode binder layer using a positive electrode binder paste containing lithium hydroxide and an organic acid as a precursor on a positive electrode substrate, a negative electrode plate manufacturing step of manufacturing a negative electrode plate by forming a negative electrode binder layer using a negative electrode binder paste added with a sodium salt as a precursor on a negative electrode substrate, and a liquid injection step of injecting a non-aqueous electrolyte containing LiBOB into a case containing an electrode body including the positive electrode plate and the negative electrode plate. In the positive electrode plate manufacturing step, a first organic acid salt composed of lithium ions derived from the lithium hydroxide and organic acid ions derived from the organic acid is formed in the positive electrode binder layer. Let the number of moles of the lithium hydroxide added in the positive electrode plate manufacturing step be A, the number of moles of the first organic acid salt formed in the positive electrode plate manufacturing step be B, and the number of moles of the sodium salt added in the negative electrode plate manufacturing step be C. Then, the values of A, B, and C satisfy 0.04 ≦ B / A ≦ 0.06 and 1.9 ≦ B / C. The first organic acid salt has a higher solubility in the non-aqueous electrolyte than a second organic acid salt composed of organic acid ions of the same kind as the organic acid ions constituting the first organic acid salt and sodium ions.

[0007] BOB ions ionized from LiBOB contained in the non-aqueous electrolyte have a slower diffusion rate than other components contained in the non-aqueous electrolyte. Therefore, immediately after injecting the non-aqueous electrolyte, sodium ions ionized from the sodium salt contained in the negative electrode mixture layer react with organic acid ions ionized from the first organic acid salt contained in the positive electrode mixture layer to form a second organic acid salt. At this time, since the first organic acid salt has a higher solubility in the non-aqueous electrolyte than the second organic acid salt, the second organic acid salt is more likely to precipitate compared to the first organic acid salt. As a result, when the BOB ions that impregnate later than other components contained in the non-aqueous electrolyte reach, the amount of sodium ions contained in the non-aqueous electrolyte becomes small. Therefore, the formation of the NaBOB film due to the reaction between sodium ions and BOB ions is suppressed. At this time, when the value of B / C, which is the ratio of the number of moles of the first organic acid salt contained in the positive electrode mixture layer to the number of moles of the sodium salt added to the negative electrode mixture paste, satisfies 1.9 ≦ B / C, the sodium ions contained in the non-aqueous electrolyte can be suitably reduced. As a result, an increase in resistance associated with the formation of the NaBOB film can be suppressed.

[0008] Also, in the positive electrode mixture paste, a part of lithium hydroxide is neutralized by reacting with an organic acid. When the content rate of lithium hydroxide in the positive electrode mixture paste is excessively high, gelation of the positive electrode mixture paste is likely to occur. On the other hand, when the content rate of the organic acid is excessively high, the thixotropy of the positive electrode mixture paste is lost, and sedimentation of the components contained in the positive electrode mixture paste is likely to occur. In that case, poor binding of the positive electrode mixture layer formed on the positive electrode plate is likely to occur. Therefore, the addition amount of the organic acid needs to be controlled so that neither gelation nor sedimentation occurs in the positive electrode mixture paste in a state where a part of lithium hydroxide is neutralized by the organic acid. B / A corresponds to the ratio of the number of moles of organic acid ions that neutralize lithium hydroxide to the number of moles of lithium hydroxide added to the positive electrode mixture paste. Therefore, when the value of B / A satisfies 0.04 ≦ B / A ≦ 0.06, it is possible to suppress gelation and sedimentation in the positive electrode mixture paste even in a state where a part of lithium hydroxide is neutralized by the organic acid.

[0009] In the above manufacturing method, it is preferable that the organic acid is acetic acid or acetic anhydride. When acetic acid or acetic anhydride is used as the organic acid, the first organic acid salt is lithium acetate and the second organic acid salt is sodium acetate. In this case, the solubility of the first organic acid salt in the non-aqueous electrolyte can be made higher than the solubility of the second organic acid salt in the non-aqueous electrolyte.

[0010] In the above manufacturing method, in the liquid injection step, it is preferable to inject the non-aqueous electrolyte at 10°C or higher and 20°C or lower. By setting the temperature of the non-aqueous electrolyte injected into the case to 20°C or lower, the solubility of the second organic acid salt in the non-aqueous electrolyte further decreases, so the precipitation of the second organic acid salt is promoted. As a result, the concentration of sodium ions in the non-aqueous electrolyte further decreases, so the formation of the NaBOB film is preferably suppressed. By setting the temperature of the non-aqueous electrolyte injected into the case to 10°C or higher, uneven impregnation of the non-aqueous electrolyte associated with excessive decrease in the fluidity of the non-aqueous electrolyte can be suppressed.

[0011] In the above manufacturing method, it is preferable that the non-aqueous electrolyte contains ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. If only ethylene carbonate is used as the solvent of the non-aqueous electrolyte, since the melting point of ethylene carbonate is high, when the temperature of the non-aqueous electrolyte is 10°C or higher and 20°C or lower, the fluidity of the non-aqueous electrolyte may be in a state of excessive decrease. In this regard, by using a non-aqueous electrolyte in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed, appropriate fluidity can be maintained even when the temperature of the non-aqueous electrolyte is 10°C or higher and 20°C or lower.

[0012] The lithium-ion secondary battery for solving the above problems is a lithium-ion secondary battery including an electrode body having a positive electrode plate and a negative electrode plate, and a non-aqueous electrolyte containing LiBOB, wherein the lithium hydroxide contained in the positive electrode plate, an organic acid component, and a sodium component, the organic acid component includes a first organic acid salt composed of an organic acid ion and a sodium ion, and at least one of the organic acid ions ionized from the first organic acid salt, and a second organic acid salt composed of the organic acid ions and sodium ions ionized from the first organic acid salt, the sodium component is the second organic acid salt, or the second organic acid salt, at least one of the sodium salt contained in the negative electrode plate, and the sodium ions ionized from the sodium salt, when the sum of the number of moles of the lithium hydroxide and the number of moles of the organic acid component is A, the number of moles of the organic acid component is B, and the number of moles of the sodium component is C, the values of A, B, and C satisfy 0.04 ≦ B / A ≦ 0.06 and 1.9 ≦ B / C, and the solubility of the first organic acid salt in the non-aqueous electrolyte is higher than that of the second organic acid salt.

[0013] According to the above configuration, by satisfying 1.9 ≦ B / C, which is the ratio of the number of moles of the organic acid component to the number of moles of the sodium component contained in the lithium-ion secondary battery, the sodium ions contained in the non-aqueous electrolyte can be suitably reduced. As a result, an increase in resistance associated with the formation of NaBOB can be suppressed. Further, by satisfying 0.04 ≦ B / A ≦ 0.06, which is the ratio of the number of moles of the organic acid component to the sum of the number of moles of lithium hydroxide and the number of moles of the organic acid component contained in the positive electrode mixture layer, it is possible to suppress gelation and sedimentation in the positive electrode mixture paste.

Advantages of the Invention

[0014] According to the present invention, in a lithium-ion secondary battery using a non-aqueous electrolyte containing LiBOB, the formation of a NaBOB film can be suppressed.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 7. [Lithium-Ion Secondary Battery] As shown in FIG. 1, the lithium-ion secondary battery 10 includes a case 11 and an electrode body 20. The case 11 has a flat bottomed rectangular outer shape with an opening on the upper side. The case 11 houses the electrode body 20 and the non-aqueous electrolyte. The lid 12 closes the opening of the case 11. The case 11 constitutes a sealed battery case in a rectangular parallelepiped shape by attaching the lid 12.

[0017] The lid body 12 is provided with a positive external terminal 13A and a negative external terminal 13B. The positive current collector part 20A, which is the end part on the positive electrode side in the electrode body 20, is electrically connected to the positive external terminal 13A via the positive current collector member 14A. The negative current collector part 20B, which is the end part on the negative electrode side in the electrode body 20, is electrically connected to the negative external terminal 13B via the negative current collector member 14B. The lid body 12 is provided with an injection port 15 for injecting a non-aqueous electrolyte. Note that the shapes of the external terminals 13A and 13B are not limited to the shapes shown in FIG. 1 and may be arbitrary shapes.

[0018] [Electrode body] As shown in FIG. 2, the electrode body 20 is a flat wound body obtained by winding a laminate in which a positive electrode plate 21, a negative electrode plate 24, and a separator 27 are laminated via the separator 27. The positive electrode plate 21, the negative electrode plate 24, and the separator 27 are laminated such that their longitudinal directions coincide with the longitudinal direction D1. The electrode body 20 has a structure in which the positive electrode plate 21 and the negative electrode plate 24 laminated with the separator 27 in between are wound around a winding axis L1 extending along the strip-shaped width direction D2.

[0019] As shown in FIG. 3, in the stacking direction D3 of the electrode body 20, the positive electrode plate 21, the separator 27, the negative electrode plate 24, and the separator 27 are stacked in this order. Note that the stacking direction D3 is a direction orthogonal to the plane including the longitudinal direction D1 and the width direction D2.

[0020] [Positive electrode plate] The positive electrode plate 21 includes a positive electrode base material 22 and a positive electrode active material layer 23. The positive electrode base material 22 is made of a metal foil composed of aluminum or an alloy mainly containing aluminum. The positive electrode active material layer 23 is provided on each of the two surfaces facing the opposite directions of the positive electrode base material 22. The positive electrode base material 22 includes a positive electrode side uncoated part 22A in which the positive electrode base material 22 is exposed without the positive electrode active material layer 23 being formed at one end in the width direction D2. The positive electrode side uncoated parts 22A provided in the positive electrode base material 22 are pressed against each other in the wound body state to form the positive electrode side current collector part 20A.

[0021] The positive electrode active material layer 23 contains a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material paste, which is a precursor of the positive electrode active material layer 23, further contains a positive electrode solvent. An example of the positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent.

[0022] As the positive electrode active material, a lithium-containing composite metal oxide capable of occluding and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10, is used. The lithium-containing composite oxide is an oxide containing lithium and another metal element other than lithium. The other metal element other than lithium is, for example, at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained as iron phosphate in the lithium-containing composite oxide. The positive electrode active material further contains excess lithium. The excess lithium is lithium hydroxide (LiOH) inevitably contained in the positive electrode active material.

[0023] For example, the lithium-containing composite oxide is lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or lithium manganate (LiMn 2 O 4 ). For example, the lithium-containing composite oxide is a ternary lithium-containing composite oxide (NCM) containing nickel, cobalt, and manganese, which is lithium nickel cobalt manganese oxide (LiNiCoMnO 2 ). For example, the lithium-containing composite oxide is lithium iron phosphate (LiFePO 4 ).

[0024] As the positive electrode conductive agent, for example, carbon black such as acetylene black (AB) and ketjen black, carbon fibers such as carbon nanotubes (CNT) and carbon nanofibers, and graphite are used. The positive electrode binder is, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA).

[0025] Note that the positive electrode plate 21 may be provided with an insulating layer at the boundary between the uncoated portion 22A on the positive electrode side and the positive electrode mixture layer 23. The insulating layer includes an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdery boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0026] [Negative electrode plate] The negative electrode plate 24 includes a negative electrode substrate 25 and a negative electrode mixture layer 26. The negative electrode substrate 25 is a metal foil made of copper or an alloy mainly composed of copper. The negative electrode mixture layer 26 is provided on each of the two surfaces facing the opposite direction of the negative electrode substrate 25. The negative electrode substrate 25 includes a negative electrode side uncoated portion 25A where the negative electrode mixture layer 26 is not formed and the negative electrode substrate 25 is exposed at one end in the width direction D2 and at an end portion located opposite to the uncoated portion 22A on the positive electrode side. In the state of the wound body, the facing portions of the negative electrode side uncoated portion 25A are pressed against each other to form the negative electrode side current collecting portion 20B.

[0027] The negative electrode mixture layer 26 includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder. Further, the negative electrode mixture paste serving as a precursor of the negative electrode mixture layer 26 further includes a negative electrode solvent. The negative electrode solvent is, for example, water.

[0028] The negative electrode active material is a material capable of occluding and releasing lithium ions. As the negative electrode active material, for example, carbon materials such as graphite, graphitizable carbon, easily graphitizable carbon, and carbon nanotubes are used. The negative electrode active material may be composite particles in which graphite particles are coated with an amorphous carbon layer.

[0029] As the negative electrode conductive agent, for example, the same materials as those for the positive electrode conductive agent can be used. As the negative electrode thickener, carboxymethyl cellulose (CMC) can be used as an example. Note that CMC is an example of an additive containing a sodium salt. Also, CMC functions as a dispersant for dispersing the negative electrode active material in the negative electrode mixture paste. The negative electrode binder is, for example, at least one selected from the group consisting of PVDF, PVA, styrene butadiene rubber (SBR), and styrene acrylic resin. Components containing sodium salts such as SBR among the negative electrode binders are examples of additives containing sodium salts.

[0030] [Separator] The separator 27 prevents contact between the positive electrode plate 21 and the negative electrode plate 24 and holds the non-aqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte penetrates from the end portion to the central portion of the separator 27.

[0031] The separator 27 is a porous non-woven fabric made of polypropylene or the like. As the separator 27, for example, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, porous polyvinyl chloride membranes, and ion conductive polymer electrolyte membranes can be used.

[0032] [Non-aqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent is, for example, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(CF 3 SO 2 ) 2 , LiC(CF3 SO 2 ) 3 is one or more lithium compounds selected from LiI and the like.

[0033] The non-aqueous electrolyte of this embodiment includes, as an example, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as non-aqueous solvents. For the non-aqueous electrolyte, it is preferable that, for example, the mass ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:1.

[0034] A film-forming agent is added to the non-aqueous electrolyte. The film-forming agent is, for example, lithium bis(oxalato)borate (LiBOB). For example, LiBOB is added to the non-aqueous electrolyte so that the concentration of LiBOB in the non-aqueous electrolyte is 0.001 or more and 0.1 or less [mol / L].

[0035] [Organic acid component] An organic acid is added to the positive electrode mixture paste in addition to the raw materials described above. The lithium ion secondary battery 10 includes an organic acid component derived from the organic acid added to the positive electrode mixture paste. The organic acid component exists in a dissolved state as ions in the non-aqueous electrolyte or exists in a state of being deposited on the electrode body 20 as an organic acid salt.

[0036] An example of the organic acid component is a first organic acid salt deposited on the positive electrode mixture layer 23 by a neutralization reaction between the organic acid added to the positive electrode mixture paste and lithium hydroxide as excess lithium. The organic acid is, for example, acetic acid (CH 3 COOH) or acetic anhydride ((CH 3 CO) 2 O). In this case, the first organic acid salt is lithium acetate (CH 3 COOLi). An example of the organic acid component is an organic acid ion ionized from the first organic acid salt described above. For example, when the organic acid is acetic acid or acetic anhydride, the organic acid ion is acetate ion (CH 3 COO -) It is. An example of the organic acid component is the second organic acid salt which is the salt of the above-described organic acid ion and sodium ion. For example, when the organic acid is acetic acid, the second organic acid salt is sodium acetate (CH 3 COONa). The sodium ion is derived from, for example, the sodium salt contained in the additive added as a negative electrode thickener to the negative electrode mixture paste.

[0037] In the lithium ion secondary battery 10, as the organic acid component, it contains at least the second organic acid salt and also contains at least one of the first organic acid salt and the organic acid ion. For example, when the positive electrode mixture layer 23 containing the first organic acid salt comes into contact with the non-aqueous electrolyte, the organic acid ion ionizes from the first organic acid salt. Note that, for example, the first organic acid salt may be present without being dissolved at a location in the positive electrode mixture layer 23 where the non-aqueous electrolyte hardly comes into contact, such as the side closer to the positive electrode substrate 22 in the positive electrode mixture layer 23. Also, all of the first organic acid salts contained in the positive electrode mixture layer 23 may be dissolved in the non-aqueous electrolyte. Then, at least a part of the organic acid ions ionized from the first organic acid salt reacts with the sodium ions to form the second organic acid salt. Note that when there are few organic acid ions ionized from the first organic acid salt, the organic acid ions ionized from the first organic acid salt may precipitate as the second organic acid salt, so that the organic acid ions may not be present in the non-aqueous electrolyte.

[0038] [Sodium component] The lithium ion secondary battery 10 contains a sodium component. The sodium component exists in the form of ions in the non-aqueous electrolyte or exists in a state of being deposited on the electrode body 20 as a sodium salt. An example of the sodium component is the sodium salt contained in the additive added to the negative electrode mixture paste. An example of the sodium component is the sodium ion ionized from the sodium salt. An example of the sodium component is the second organic acid salt which is the salt of the sodium ion and the organic acid ion. That is, the second organic acid salt is both an organic acid component and a sodium component.

[0039] The lithium-ion secondary battery 10 contains at least a second organic acid salt as a sodium component. Note that the lithium-ion secondary battery 10 may contain at least one of a sodium salt and sodium ions added to the negative electrode binder paste together with the second organic acid salt as the sodium component. For example, when the negative electrode binder layer 26 containing the sodium salt comes into contact with the non-aqueous electrolyte, sodium ions are ionized from the sodium salt. Note that the sodium salt may be present without dissolving at a location in the negative electrode binder layer 26 where it is difficult for the non-aqueous electrolyte to come into contact, such as on the side closer to the negative electrode substrate 25 in the negative electrode binder layer 26. Also, all of the sodium salt contained in the negative electrode binder layer 26 may dissolve in the non-aqueous electrolyte. Then, at least a part of the sodium ions ionized from the sodium salt reacts with acetate ions to form a second organic acid salt. Note that all of the sodium ions ionized from the sodium salt may precipitate as the second organic acid salt, so that no sodium ions may be present in the non-aqueous electrolyte. Also, sodium ions may be present in the non-aqueous electrolyte when, for example, the organic acid ions ionized from the first organic acid salt are locally scarce.

[0040] [Method for manufacturing a lithium-ion secondary battery] As shown in FIG. 4, the method for manufacturing the lithium-ion secondary battery 10 includes steps S1 to S4. Step S1 is a positive electrode plate manufacturing step for manufacturing the positive electrode plate 21. The positive electrode plate manufacturing step of step S1 includes a step of manufacturing a positive electrode binder paste by kneading raw materials of the positive electrode binder paste, and a step of forming a positive electrode binder layer 23 by drying the positive electrode binder paste applied to the positive electrode substrate 22 and then pressing it to an appropriate thickness. Through the above steps, the positive electrode plate 21 is manufactured.

[0041] Step S2 is a negative electrode plate manufacturing process for manufacturing the negative electrode plate 24. The negative electrode plate manufacturing process in Step S2 includes a process of manufacturing a negative electrode mixture paste by kneading raw materials of the negative electrode mixture paste, and a process of forming a negative electrode mixture layer 26 by drying the negative electrode mixture paste applied to the negative electrode substrate 25 and then pressing it to an appropriate thickness. Through the above processes, the negative electrode plate 24 is manufactured. Note that the order of performing Step S1 and Step S2 is not particularly limited. For example, Step S1 may be performed after Step S2, or Step S1 and Step S2 may be performed in parallel.

[0042] Step S3 is a process of manufacturing the electrode body 20 using the positive electrode plate 21, the negative electrode plate 24, and the separator 27. In Step S3, first, the positive electrode plate 21 and the negative electrode plate 24 are wound in a state of being laminated via the separator 27, and then further pressed flat. Next, the uncoated portion 22A on the positive electrode side is pressure-welded to form the positive electrode current collector portion 20A. Similarly, the uncoated portion 25A on the negative electrode side is pressure-welded to form the negative electrode current collector portion 20B. Through the above procedures, the electrode body 20 is manufactured.

[0043] Step S4 includes a process of housing the electrode body 20 in the case 11 and a liquid injection process of injecting a non-aqueous electrolyte. In Step S4, the positive electrode current collector portion 20A is electrically connected to the external terminal 13A of the positive electrode via the positive electrode current collector member 14A. The negative electrode current collector portion 20B is electrically connected to the external terminal 13B of the negative electrode via the negative electrode current collector member 14B. The opening at the upper part of the case 11 is closed by the lid body 12. Then, after drying the electrode body 20 housed in the case 11, a non-aqueous electrolyte is injected. The temperature of the non-aqueous electrolyte to be injected is preferably 10°C or higher and 20°C or lower. Thereafter, the lithium-ion secondary battery 10 is manufactured through an aging process and an initial charging process.

[0044] [Actions of the Embodiment] Hereinafter, the actions of this embodiment will be described with reference to FIGS. 5 to 7. [Reactions Occurring in the Positive Electrode Mixture Paste] Figure 5 schematically shows the state when the positive electrode mixture paste 23P is kneaded in step S1. In the positive electrode mixture paste 23P, a positive electrode active material 31 and acetic acid 33 which is an example of an organic acid are added as raw materials. The positive electrode active material 31 contains lithium hydroxide 32 as excess lithium.

[0045] In the positive electrode mixture paste 23P, a part of the lithium hydroxide 32 is neutralized by the acetic acid 33, thereby generating lithium acetate 34 which is an example of a first organic acid salt. That is, in the positive electrode mixture paste 23P, lithium acetate 34 is generated by the reaction between lithium ions 32A ionized from the lithium hydroxide 32 and acetate ions 33A ionized from the acetic acid 33. Lithium acetate 34 is a salt composed of lithium ions 32A and acetate ions 33A. Further, the acetate ion 33A is an example of an organic acid ion constituting the lithium acetate 34.

[0046] In the positive electrode mixture paste 23P, when the content rate of the lithium hydroxide 32 is excessively high, the positive electrode mixture paste 23P is likely to gel. On the other hand, when the content rate of the acetic acid 33 is excessively high, the thixotropy of the positive electrode mixture paste 23P is lost, and sedimentation of the components contained in the positive electrode mixture paste 23P is likely to occur. In that case, poor binding of the positive electrode mixture layer 23 formed on the positive electrode plate 21 is likely to occur. Therefore, the addition amount of the acetic acid 33 in the positive electrode mixture paste 23P needs to be controlled so that neither gelation nor sedimentation occurs in the positive electrode mixture paste 23P in a state where a part of the lithium hydroxide 32 is neutralized by the acetic acid 33.

[0047] In the positive electrode plate manufacturing process of step S1, let the number of moles of the lithium hydroxide 32 added to the positive electrode mixture paste 23P be A [mol]. Further, in the positive electrode plate manufacturing process, let the number of moles of the lithium acetate 34 formed in the positive electrode mixture layer 23 by the reaction between the lithium ions 32A ionized from the lithium hydroxide 32 and the acetate ions 33A ionized from the acetic acid 33 be B [mol]. At this time, the addition amount of the acetic acid 33 is determined so that the value of B / A satisfies 0.04 ≦ B / A ≦ 0.06.

[0048] By satisfying the condition 0.04 ≤ B / A, gelation of the positive electrode mixture paste 23P associated with an excessively high content of lithium hydroxide 32 can be suppressed. Also, by satisfying the condition B / A ≤ 0.06, sedimentation of the components contained in the positive electrode mixture paste 23P associated with an excessively low content of lithium hydroxide 32 can be suppressed. Therefore, by satisfying the condition 0.04 ≤ B / A ≤ 0.06, even when a part of lithium hydroxide 32 is neutralized by acetic acid 33, it is possible to suppress gelation and sedimentation in the positive electrode mixture paste 23P.

[0049] [Reaction occurring immediately after injecting the non-aqueous electrolyte] FIG. 6 schematically shows the state immediately after injecting the non-aqueous electrolyte EL into the case 11 in step S4, in which the electrode body 20 is impregnated with the non-aqueous electrolyte EL. BOB ions ionized from LiBOB contained in the non-aqueous electrolyte EL have a slower ion diffusion rate compared to other components contained in the non-aqueous electrolyte EL. Therefore, in the state immediately after injecting the non-aqueous electrolyte EL, components other than BOB ions contained in the non-aqueous electrolyte EL impregnate the electrode body 20. Note that, in the state of the electrode body 20 before injecting the non-aqueous electrolyte EL, the positive electrode mixture layer 23 contains a positive electrode active material 31, lithium hydroxide 32, and lithium acetate 34. Also, in the state of the electrode body 20 before injecting the non-aqueous electrolyte EL, the negative electrode mixture layer 26 contains a negative electrode active material 41 and a sodium salt 42.

[0050] When the electrode body 20 is impregnated with the non-aqueous electrolyte EL, lithium ions 32A and acetate ions 33A are ionized from lithium acetate 34 contained in the positive electrode mixture layer 23. Also, sodium ions 42A are ionized from the sodium salt 42 in the negative electrode mixture layer 26. Then, by the reaction of acetate ions 33A and sodium ions 42A, sodium acetate 50 is generated. Sodium acetate 50 is a salt composed of acetate ions 33A and sodium ions 42A. Sodium acetate 50 is a salt containing an organic acid ion of the same kind as acetate ions 33A, which are the organic acid ions constituting lithium acetate 34.

[0051] Since lithium acetate 34 has a higher solubility in the non-aqueous electrolyte EL than sodium acetate 50, sodium acetate 50 is more likely to precipitate compared to lithium acetate 34. As a result, the state of the non-aqueous electrolyte EL contains less sodium ions 42A.

[0052] [State after BOB ions reach] Figure 7 schematically shows the state after injecting the non-aqueous electrolyte EL into the case 11 in step S4, where the BOB ions 51 contained in the non-aqueous electrolyte EL reach late. As described above, when the BOB ions 51 contained in the non-aqueous electrolyte EL reach late, the sodium salt 42 contained in the negative electrode mixture layer 26 precipitates as sodium acetate 50. Therefore, the state of the non-aqueous electrolyte EL contains less sodium ions 42A. Thus, the formation of the NaBOB film due to the reaction between the sodium ions 42A and the BOB ions 51 can be suppressed.

[0053] In the negative electrode plate manufacturing process of step S2, let the number of moles of the sodium salt 42 added to the negative electrode mixture paste be C [mol]. At this time, the addition amount of acetic acid 33 is determined so that the value of B / C, which is the ratio of the number of moles of lithium acetate 34 generated in the positive electrode mixture paste 23P to the number of moles of the sodium salt 42 added to the negative electrode mixture paste, satisfies 1.9 ≤ B / C. Therefore, the addition amount of acetic acid 33 to the positive electrode mixture paste 23P is determined so that the values of A, B, and C satisfy 0.04 ≤ B / A ≤ 0.06 and 1.9 ≤ B / C. By satisfying 1.9 ≤ B / C, the increase in resistance associated with the formation of NaBOB can be preferably suppressed.

[0054] In the electrolyte injection step of step S4, by setting the temperature of the non-aqueous electrolyte EL injected into the case 11 to 20°C or lower, the solubility of sodium acetate 50 in the non-aqueous electrolyte EL further decreases, so the precipitation of sodium acetate 50 is promoted. As a result, since the concentration of sodium ions 42A in the non-aqueous electrolyte EL further decreases, the formation of the NaBOB film is preferably suppressed. By setting the temperature of the non-aqueous electrolyte EL injected into the case 11 to 10°C or higher, uneven impregnation of the non-aqueous electrolyte EL associated with excessive decrease in the fluidity of the non-aqueous electrolyte EL can be suppressed.

[0055] If only ethylene carbonate is used as the non-aqueous solvent, since the melting point of ethylene carbonate is high, when the temperature of the non-aqueous electrolyte EL is 10°C or higher and 20°C or lower, the fluidity of the non-aqueous electrolyte EL may be in a state of excessive decrease. In this regard, by using a non-aqueous electrolyte EL in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed as the non-aqueous solvent, even when the temperature of the non-aqueous electrolyte EL is 10°C or higher and 20°C or lower, appropriate fluidity can be maintained.

[0056] [Regarding the values of A to C] Hereinafter, the value of A [mol], which is the number of moles of lithium hydroxide 32 added to the positive electrode mixture paste 23P, will be described in detail. The value of A can be measured by titration such as the Winkler method with respect to the lithium hydroxide 32 contained in the positive electrode active material 31 used as a raw material.

[0057] In the positive electrode mixture layer 23 formed in the positive electrode plate manufacturing step of step S1, a part of the lithium hydroxide 32 added to the positive electrode mixture paste 23P is neutralized by acetic acid 33. Therefore, the value of A corresponds to the sum of the number of moles of lithium hydroxide 32 not neutralized by acetic acid 33 and the number of moles of lithium hydroxide 32 neutralized by acetic acid 33 among the lithium hydroxide 32 added to the positive electrode mixture paste 23P. In other words, the value of A corresponds to the sum of the number of moles of lithium hydroxide 32 contained in the positive electrode mixture layer 23 and the number of moles of lithium acetate 34. Note that the organic acid component contained in the positive electrode mixture layer 23 formed in the positive electrode plate manufacturing step of step S1 is lithium acetate 34.

[0058] In the state of the lithium ion secondary battery 10, the value of A corresponds to the sum of the number of moles of lithium hydroxide 32 contained in the positive electrode mixture layer 23 and the number of moles of the organic acid component contained in the lithium ion secondary battery 10 in the state of the lithium ion secondary battery 10. The organic acid component contained in the lithium ion secondary battery 10 is at least one of acetate ion 33A and lithium acetate 34, and sodium acetate 50. That is, all of the lithium acetate 34 formed in the positive electrode mixture layer 23 in the positive electrode plate manufacturing process may be dissolved in the non-aqueous electrolyte EL in the state of the lithium ion secondary battery 10, or a part thereof may be present in the positive electrode mixture layer 23 without being dissolved. Further, all of the acetate ions 33A ionized from lithium acetate 34 may be precipitated as sodium acetate 50, or may be present in the non-aqueous electrolyte EL.

[0059] Note that in the state of the lithium ion secondary battery 10, the value of A can be measured by separately measuring the number of moles of lithium hydroxide 32 contained in the positive electrode mixture layer 23 and the number of moles of the organic acid component. For example, the number of moles of lithium hydroxide 32 contained in the positive electrode mixture layer 23 in the state of the lithium ion secondary battery 10 can be measured by titration such as the Winkler method. Further, the number of moles of the organic acid component contained in the lithium ion secondary battery 10 can be measured by performing titration such as the Winkler method after dissolving all the organic acid components in the non-aqueous electrolyte EL by raising the temperature of the non-aqueous electrolyte EL.

[0060] Next, the value of B [mol], which is the number of moles of lithium acetate 34 formed in the positive electrode active material layer 23 in the positive electrode plate manufacturing process of step S1, will be described in detail. The value of B corresponds to the ratio of the number of moles of acetate ions 33A that neutralize lithium hydroxide 32 contained in the positive electrode active material paste 23P. For example, when acetic acid 33 is used as the organic acid, 1 mol of acetate ions 33A is ionized from 1 mol of acetic anhydride. Therefore, the number of moles B [mol] of lithium acetate 34 formed in the positive electrode active material layer 23 in the positive electrode plate manufacturing process is equal to the number of moles of acetic acid 33 added to the positive electrode active material paste 23P. For example, when acetic anhydride is used as the organic acid, 2 mol of acetate ions 33A is ionized from 1 mol of acetic anhydride. Therefore, the number of moles B [mol] of lithium acetate 34 formed in the positive electrode active material layer 23 in the positive electrode plate manufacturing process is twice the number of moles of acetic anhydride added to the positive electrode active material paste 23P. Therefore, the value of B can be calculated from the addition amount (number of moles) of the organic acid added to the positive electrode active material paste 23P.

[0061] In the state of the lithium ion secondary battery 10, the value of B corresponds to the number of moles of the organic acid component contained in the lithium ion secondary battery 10 in the state of the lithium ion secondary battery 10. Therefore, the value of A corresponds to the sum of the number of moles of lithium hydroxide 32 contained in the positive electrode active material layer 23 and the value of B in the state of the lithium ion secondary battery 10. Note that the value of B in the lithium ion secondary battery 10 can be measured by performing titration such as the Winkler method after dissolving all the organic acid components in the non-aqueous electrolyte EL by raising the temperature of the non-aqueous electrolyte EL as described above.

[0062] Next, the value of C [mol], which is the number of moles of the sodium salt 42 added to the negative electrode active material paste in the negative electrode plate manufacturing process of step S2, will be described in detail. Note that the value of C can be measured, for example, by performing inductively coupled plasma (ICP) emission spectrometry on a sample obtained by cutting out a part of the negative electrode active material layer 26.

[0063] In the state of the lithium ion secondary battery 10, the value of C corresponds to the number of moles of the sodium component contained in the lithium ion secondary battery 10 in the state of the lithium ion secondary battery 10. The sodium component contained in the lithium ion secondary battery 10 is at least sodium acetate 50. The lithium ion secondary battery 10 may further contain at least one of a sodium salt 42 and sodium ions 42A as the sodium component. In other words, the sodium component contained in the lithium ion secondary battery 10 is sodium acetate 50, or, in addition to sodium acetate 50, at least one of a sodium salt 42 and sodium ions 42A. That is, all of the sodium salt 42 added to the negative electrode mixture paste in the negative electrode plate manufacturing process may dissolve in the non-aqueous electrolyte EL, and all of the sodium ions 42A ionized from the sodium salt 42 may precipitate as sodium acetate 50. Also, a part of the sodium ions 42A ionized from the sodium salt 42 may be present in the non-aqueous electrolyte EL, or a part of the sodium salt 42 contained in the negative electrode mixture layer 26 may be present in the negative electrode mixture layer 26 without dissolving.

[0064] Note that the value of C in the lithium ion secondary battery 10 can be measured by performing inductively coupled plasma (ICP) emission spectrometry after bringing all the sodium components into a state of being dissolved in the non-aqueous electrolyte EL by raising the temperature of the non-aqueous electrolyte EL. That is, the value of C corresponds to the number of moles of sodium element contained in the sodium component, or in other words, it corresponds to the number of moles of sodium element contained in the sodium salt 42 added in the negative electrode plate manufacturing process.

[0065] [Effects of Embodiment] According to the above embodiment, the following effects can be obtained. (1) By adding acetic acid 33 to the positive electrode active material paste 23P, lithium acetate 34 is formed in the positive electrode active material layer 23. When the non-aqueous electrolyte EL is injected in this state, sodium ions 42A ionized from the sodium salt 42 contained in the negative electrode active material layer 26 react with acetate ions 33A ionized from lithium acetate 34 to produce sodium acetate 50. At this time, since lithium acetate 34 has a higher solubility in the non-aqueous electrolyte EL than sodium acetate 50, sodium acetate 50 is more likely to precipitate compared to lithium acetate 34. As a result, when the BOB ions 51 that impregnate later than other components contained in the non-aqueous electrolyte EL reach, the state of the non-aqueous electrolyte EL contains less sodium ions 42A. Therefore, the formation of the NaBOB film due to the reaction between the sodium ions 42A and the BOB ions 51 can be suppressed.

[0066] (2) By satisfying 1.9 ≦ B / C for the value of B / C, the sodium ions 42A contained in the non-aqueous electrolyte EL can be suitably reduced. As a result, an increase in resistance associated with the formation of the NaBOB film can be suppressed.

[0067] (3) By satisfying 0.04 ≦ B / A ≦ 0.06 for the value of B / A, even in a state where a part of lithium hydroxide 32 is neutralized by acetic acid 33, it is possible to suppress gelation and sedimentation in the positive electrode active material paste 23P.

[0068] (4) When acetic acid 33 is used as the organic acid, the first organic acid salt is lithium acetate 34 and the second organic acid salt is sodium acetate 50. In this case, the solubility of the first organic acid salt in the non-aqueous electrolyte EL can be made higher than the solubility of the second organic acid salt in the non-aqueous electrolyte EL. The same applies when acetic anhydride is used as the organic acid.

[0069] (5) By setting the temperature of the non-aqueous electrolyte EL injected into the case 11 to 20 °C or lower, the precipitation of sodium acetate 50 is promoted, so that the formation of the NaBOB film is preferably suppressed. Further, by setting the temperature of the non-aqueous electrolyte EL injected into the case 11 to 10 °C or higher, uneven impregnation of the non-aqueous electrolyte EL due to excessive decrease in the fluidity of the non-aqueous electrolyte EL can be suppressed.

[0070] (6) By using a non-aqueous electrolyte EL containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as the non-aqueous solvent, appropriate fluidity can be maintained even when the temperature of the non-aqueous electrolyte EL is 10 °C or higher and 20 °C or lower.

[0071] [Modified Example] Note that the above embodiment can be implemented with the following modifications. Also, the following modified examples can be combined within a technically consistent range.

[0072] · When the fluidity of the non-aqueous electrolyte EL is in an appropriate state when the temperature of the non-aqueous electrolyte EL is 10 °C or higher and 20 °C or lower, the type of the non-aqueous solvent is not limited. For example, any of the non-aqueous solvents exemplified in the embodiment may be used. Also, even when ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are used as the non-aqueous solvent, the mass ratio thereof is not limited to 1:1:1. The mass ratio of the non-aqueous solvent in this case may be appropriately determined so that the fluidity of the non-aqueous electrolyte EL is in an appropriate state when the temperature of the non-aqueous electrolyte EL is 10 °C or higher and 20 °C or lower.

[0073] · The temperature of the non-aqueous electrolyte EL injected into the case 11 may be appropriately changed according to the type of the non-aqueous solvent. For example, if sodium acetate 50 precipitates sufficiently, the temperature of the non-aqueous electrolyte EL may exceed 20 °C. For example, if the fluidity of the non-aqueous electrolyte EL is properly maintained, the temperature of the non-aqueous electrolyte EL may be less than 10 °C.

[0074] ·Although the case where acetic acid 33 or acetic anhydride is used as the organic acid is exemplified, the type of the organic acid is not limited thereto. The organic acid may be any acid as long as the solubility of the organic acid in the non-aqueous electrolyte EL in the first organic acid salt, which is a salt of lithium and the organic acid, is higher than the solubility of the organic acid in the non-aqueous electrolyte EL in the second organic acid salt, which is a salt of sodium and the organic acid. The organic acid may be, for example, citric acid, or acetic acid 33 or acetic anhydride and citric acid may be combined. Therefore, the organic acid is, for example, at least one selected from the group consisting of acetic acid 33, acetic anhydride, and citric acid.

[0075] ·The lithium ion secondary battery 10 may be mounted on a computer, other electronic devices, in addition to an automatic transporter, a special vehicle for cargo handling, an electric vehicle, a hybrid vehicle, etc., or may constitute other systems. For example, it may be provided in a moving body such as a ship or an aircraft, or may be a power supply system that supplies power to a building or a home where a secondary battery is installed via a substation from a power plant.

[0076] [Examples] Hereinafter, with reference to FIGS. 8 and 9, Examples 1 to 8 and Comparative Examples 1 to 10 will be described. Note that the following examples are an example for explaining the effects of the above-described embodiment, and do not limit the present invention.

[0077] [Preparation of Samples] In Examples 1 to 8 and Comparative Examples 1 to 10, after manufacturing the lithium ion secondary battery 10 by the steps of Steps S1 to S4, aging and initial charging were performed. Acetic acid 33 was used as the organic acid. The concentration of LiBOB in the non-aqueous electrolyte EL was 0.003 [mol / L]. Note that in Comparative Example 1, the lithium ion secondary battery 10 was manufactured without adding acetic acid 33 to the positive electrode mixture paste 23P. Further, in Comparative Examples 5, 6, 8, and 9, in the positive electrode plate manufacturing step of Step S1, the manufacturing of the lithium ion secondary battery 10 was stopped at the stage of manufacturing the positive electrode plate 21.

[0078] After measuring the number of moles of lithium hydroxide 32 contained in the positive electrode active material 31 per unit weight in the state of the raw material, the value of A was calculated from the basis weight of the positive electrode mixture layer 23. Further, the value of B was calculated from the addition amount of acetic acid 33. Then, in step S2, a part of the negative electrode mixture layer 26 was cut out from the negative electrode plate 24 on which the negative electrode mixture layer 26 was formed, and after measuring the amount of sodium element contained in the negative electrode mixture layer 26 per unit weight, the value of C was calculated from the basis weight of the negative electrode mixture layer 26. The values of A to C, the value of B / A, and the value of B / C in Examples 1 to 8 and Comparative Examples 1 to 10 are shown in FIG. 8.

[0079] [Example 1] As shown in FIG. 8, in Example 1, the value of A was 0.687 [mol], the value of B was 0.034 [mol], the value of C was 0.010 [mol], the value of B / A was 0.050, and the value of B / C was 3.57.

[0080] [Example 2] In Example 2, the value of A was 0.687 [mol], the value of B was 0.034 [mol], the value of C was 0.012 [mol], the value of B / A was 0.050, and the value of B / C was 2.85.

[0081] [Example 3] In Example 3, the value of A was 0.834 [mol], the value of B was 0.034 [mol], the value of C was 0.014 [mol], the value of B / A was 0.041, and the value of B / C was 2.45.

[0082] [Example 4] In Example 4, the value of A was 0.667 [mol], the value of B was 0.034 [mol], the value of C was 0.014 [mol], the value of B / A was 0.051, and the value of B / C was 2.45.

[0083] [Example 5] In Example 5, the value of A was 0.655 [mol], the value of B was 0.034 [mol], the value of C was 0.014 [mol], the value of B / A was 0.052, and the value of B / C was 2.45.

[0084] [Example 6] In Example 6, the value of A was 0.687 [mol], the value of B was 0.034 [mol], the value of C was 0.015 [mol], the value of B / A was 0.050, and the value of B / C was 2.25.

[0085] [Example 7] In Example 7, the value of A was 0.667 [mol], the value of B was 0.027 [mol], the value of C was 0.014 [mol], the value of B / A was 0.041, and the value of B / C was 2.00.

[0086] [Example 8] In Example 8, the value of A was 0.687 [mol], the value of B was 0.034 [mol], the value of C was 0.018 [mol], the value of B / A was 0.050, and the value of B / C was 1.91.

[0087] [Comparative Example 1] In Comparative Example 1, the value of A was 0.533 [mol], and the value of C was 0.383 [mol], which was 1.91. Since acetic acid 33 was not added in Comparative Example 1, the values of B, B / A, and B / C were all 0 [mol].

[0088] [Comparative Example 2] In Comparative Example 2, the value of A was 0.687 [mol], the value of B was 0.034 [mol], the value of C was 0.070 [mol], the value of B / A was 0.050, and the value of B / C was 0.49.

[0089] [Comparative Example 3] In Comparative Example 3, the value of A was 0.687 [mol], the value of B was 0.045 [mol], the value of C was 0.389 [mol], the value of B / A was 0.066, and the value of B / C was 0.12.

[0090] [Comparative Example 4] In Comparative Example 4, the value of A was 0.687 [mol], the value of B was 0.034 [mol], the value of C was 0.516 [mol], the value of B / A was 0.050, and the value of B / C was 0.07.

[0091] [Comparative Examples 5 and 6] In Comparative Example 5 and Comparative Example 6, the value of A was 0.802 [mol], the value of B was 0.056 [mol], and the value of B / A was 0.070. Note that Comparative Example 5 and Comparative Example 6 are samples at the same level but different.

[0092] [Comparative Example 7] In Comparative Example 7, the value of A was 0.821 [mol], the value of B was 0.059 [mol], the value of C was 0.014 [mol], the value of B / A was 0.072, and the value of B / C was 4.24.

[0093] [Comparative Example 8] In Comparative Example 8, the value of A was 0.821 [mol], the value of B was 0.014 [mol], and the value of B / A was 0.017.

[0094] [Comparative Example 9] In Comparative Example 9, the value of A was 0.821 [mol], the value of B was 0.027 [mol], and the value of B / A was 0.033.

[0095] [Comparative Example 10] In Comparative Example 10, the value of A was 0.821 [mol], the value of B was 0.030 [mol], the value of C was 0.011 [mol], the value of B / A was 0.037, and the value of B / C was 2.74.

[0096] [Evaluation] In the manufacturing process of the lithium-ion secondary battery 10, it was confirmed whether or not the gelation of the positive electrode mixture paste 23P occurred. Also, in the manufacturing process of the lithium-ion secondary battery 10, it was confirmed whether or not the positive electrode mixture layer 23 peeled off from the positive electrode substrate 22 in the positive electrode plate 21. Then, after measuring the reaction resistance of the lithium-ion secondary battery 10 after the first charge in each example and each comparative example, based on the reaction resistance of Comparative Example 1 without the addition of acetic acid 33, the ratio of the reaction resistance of each example and each comparative example to the reaction resistance of Comparative Example 1 was calculated. The evaluation results are shown in FIG. 8. Also, the relationship between the value of B / C and the ratio of the reaction resistance of each example and each comparative example to the reaction resistance of Comparative Example 1 is shown in FIG. 9.

[0097] [Gelation of Cathode Active Material Paste and Peeling of Cathode Active Material Layer] As shown in FIG. 8, in Examples 1 to 8 and Comparative Examples 1 to 7, gelation of the cathode active material paste 23P was not confirmed. On the other hand, gelation of the cathode active material paste 23P was confirmed in Comparative Examples 8 to 10 where the value of B / A was less than 0.04.

[0098] In Examples 1 to 8, Comparative Examples 1 to 4, and Comparative Examples 8 to 10, peeling of the cathode active material layer 23 in the cathode plate 21 was not confirmed. On the other hand, peeling of the cathode active material layer 23 in the cathode plate 21 was confirmed in Comparative Examples 5 to 7 where the value of B / A was 0.07 or more.

[0099] From the above results, it was confirmed that by satisfying 0.04 ≤ B / A ≤ 0.06, even when a part of lithium hydroxide 32 was neutralized by acetic acid 33, it was possible to suppress gelation and sedimentation in the cathode active material paste 23P.

[0100] [Reaction Resistance] The graph shown in FIG. 9 has the value of B / C on the horizontal axis and represents the ratio of the reaction resistance of each example and each comparative example based on Comparative Example 1 on the vertical axis. The points P1 to P8 shown in the graph correspond to the results of Examples 1 to 8 in the order from point P1 to point P8. The points PC1 to PC4 shown in the graph correspond to the results of Comparative Examples 1 to 4 in the order from point PC1 to point PC4. The point PC7 shown in the graph corresponds to the result of Comparative Example 7. The point PC10 shown in the graph corresponds to the result of Comparative Example 10.

[0101] As shown in FIG. 9, it was confirmed that in Examples 1 to 8 where the value of B / C was 1.9 or more, the reaction resistance was lower than that of Comparative Example 1. And it was confirmed that the reaction resistance tended to decrease more as the value of B / C increased. In addition, it was confirmed that the reaction resistance was also smaller than that of Comparative Example 1 in Comparative Example 7 and Comparative Example 10 where the value of B / C was 1.9 or more.

[0102] On the other hand, in Comparative Examples 2 to 4 where the B / C value is less than 1.9, it was confirmed that the reaction resistance increased in all cases compared to Comparative Example 1. From the above results, it was confirmed that by setting the B / C value to 1.9 or more, an increase in resistance associated with the formation of the NaBOB film can be suppressed.

Explanation of Reference Numerals

[0103] EL…Non-aqueous electrolyte 10…Lithium-ion secondary battery 11…Case 20…Electrode assembly 21…Positive electrode plate 22…Positive electrode substrate 23…Positive electrode active material layer 23P…Positive electrode active material paste 24…Negative electrode plate 25…Negative electrode substrate 26…Negative electrode active material layer 27…Separator 31…Positive electrode active material 32…Lithium hydroxide 32A…Lithium ion 33…Acetic acid 33A…Acetate ion 34…Lithium acetate 41…Negative electrode active material 42…Sodium salt 42A…Sodium ion 50…Sodium acetate 51…BOB ion

Claims

1. a positive electrode plate manufacturing process in which a positive electrode mixture layer is formed on a positive electrode substrate using a positive electrode mixture paste as a precursor, the positive electrode mixture paste being added with a positive electrode active material containing lithium hydroxide and a lithium-containing composite metal oxide and an organic acid, which is acetic acid or acetic anhydride; a negative electrode plate manufacturing process for manufacturing a negative electrode plate by forming a negative electrode mixture layer on a negative electrode substrate using a negative electrode mixture paste containing a sodium salt as a precursor; A liquid injection process of injecting a nonaqueous electrolyte solution containing LiBOB into a case that houses an electrode assembly including the positive electrode plate and the negative electrode plate, In the positive electrode plate manufacturing step, a first organic acid salt is formed in the positive electrode mixture layer, the first organic acid salt being composed of lithium ions derived from the lithium hydroxide and organic acid ions derived from the organic acid, The number of moles of the lithium hydroxide added in the positive electrode plate manufacturing process is A, The number of moles of the first organic acid salt formed in the positive electrode plate production process is B, When the number of moles of sodium element contained in the sodium salt added in the negative electrode plate manufacturing process is C, The values ​​of A, B, and C satisfy 0.04≦B / A≦0.06 and 1.9≦B / C, The first organic acid salt has a higher solubility in the nonaqueous electrolyte than a second organic acid salt that is composed of an organic acid ion of the same type as an organic acid ion constituting the first organic acid salt and a sodium ion. A method for manufacturing a lithium-ion secondary battery.

2. In the liquid injection step, the nonaqueous electrolyte is injected at a temperature of 10° C. or higher and 20° C. or lower. The method for producing the lithium ion secondary battery according to claim 1 .

3. The non-aqueous electrolyte contains ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The method for producing the lithium ion secondary battery according to claim 2 .

4. A lithium ion secondary battery comprising: an electrode assembly including a positive electrode plate and a negative electrode plate, the positive electrode plate including a positive electrode active material including a lithium-containing composite metal oxide; and a non-aqueous electrolyte solution including LiBOB, The positive electrode plate includes lithium hydroxide, an organic acid component, and a sodium component, the organic acid component is a first organic acid salt including an organic acid ion, which is an acetate ion, and a lithium ion, and a second organic acid salt including at least one of the organic acid ions ionized from the first organic acid salt, the organic acid ion ionized from the first organic acid salt, and a sodium ion; The sodium component is the second organic acid salt, or the second organic acid salt, and at least one of a sodium salt contained in the negative electrode plate and a sodium ion ionized from the sodium salt; The sum of the number of moles of the lithium hydroxide and the number of moles of the organic acid component is A, The number of moles of the organic acid component is B, If the number of moles of sodium element contained in the sodium component is C, The values ​​of A, B, and C satisfy 0.04≦B / A≦0.06 and 1.9≦B / C, The first organic acid salt has a higher solubility in the nonaqueous electrolyte than the second organic acid salt. Lithium-ion secondary battery.

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